A signal includes informational content and characteristics other than informational content. For example, an optical signal may have an optical power level, which is a measure of the energy delivered by the optical signal per unit of time. In another example, an electrical signal may have a signal-to-noise ratio, which reflects the relative amounts of signal and noise in a transmission. These signal characteristics that do not represent the informational content of the signal are referred to as parametric information, and may be represented by data, called parametric data.